This invention relates to the measurement of currents in an operating circuit and, in particular, to the measurement of such currents without breaking the circuit.
The most straightforward method of measuring the electrical current in an operating circuit is to break the circuit at some point and insert a current measuring device such as a current meter. The circuit is then reestablished through the current measuring device and the current measured.
Breaking the circuit and inserting the measuring device is typically inconvenient at best and often very difficult. In the case of an electronic circuit on a printed circuit board, for example, it may involve cutting circuit traces or unsoldering components.
In the case of ac currents, it is common to sense large current inductively in order to avoid the problems of inserting the measuring device into the circuit. Unfortunately, this is of little help for small ac currents and for dc currents.
DC currents are sometimes sensed with magnetic sensors such as Hall-effect devices. This avoids the problems of inserting the measurement device into the circuit. Unfortunately, this method works poorly for small currents and it is difficult to get reliable and accurate results.